1. Field of the Invention
The present invention relates to a wire-wound inductor and, more particularly, to a surface-mounting-type, high-frequency wire-wound inductor for use in a choke coil, a transformer, and a coil.
2. Description of the Related Art
The construction of a conventional wire-wound inductor of this type is shown in FIG. 7 through FIG. 9. A wire-wound inductor 1 includes a square-flanged core member 2 constructed of a drum-like magnetic material, and a cylindrical case core member 3 as shown in an elevational sectional view in FIG. 7 and an exploded perspective view in FIG. 8. The square-flanged core member 2 includes a cylindrical wire-wound portion 6 around which a coil 4 is wound.
The cylindrical wire-wound portion 6 is provided with an upper square flange 7 and a lower square flange 8 on its top and bottom ends, respectively. The coil 4 is wound between the flanges 7 and 8. The cylindrical wire-wound portion 6 of the square-flanged core member 2 around which the coil 4 is wound is disposed inside of the case core member 3. A square opening 9 on the top side of the case core member 3 receives the upper flange 7 of the square-flanged core member 2, and an adhesive is applied to adhere the case core member 3 and the upper flange 7. The lower surface of the case core member 3 is in contact with the top surface of the lower flange 8 of the square-flanged core member 2 so that the case core member 3 is mounted on the lower flange 8. The core members 2 and 3 constitute a magnetic path of a magnetic flux generated by the coil 4. Terminal electrodes (not shown) are formed on the lower flange 8, and the ends of the coil 4 are connected to the terminal electrodes via soldering or a thermal compression bonding technique.
In the wire-wound inductor 1, the upper flange 7 of the square-flanged core member 2 is typically slightly smaller in dimension than the opening 9 of the case core member 3 so that the upper flange 7 is smoothly inserted into the opening 9. Thus, a gap g (see FIG. 7 and FIG. 9) is created between the square opening 9 and the upper flange 7. In the conventional wire-wound inductor 1, variations occur in the contact state between the upper flange 7 and the case core member 3. Specifically, when the center of the upper flange 7 is aligned with the center of the square opening 9 as shown in FIG. 10A, the upper flange 7 does not contact the case core member 3. When the center of the upper flange 7 is offset from the center of the square opening 9 as shown in FIG. 10B and FIG. 10C, the outer surface of the upper flange 7 touches one or two inner surfaces of the case core member 3 in a surface contact manner such that entire side surfaces of the upper flange 7 contact entire inner side surfaces of the case core member 3. When the upper flange 7 is disposed in a rotated state with respect to the square opening 9 as shown in FIG. 10D, the upper flange 7 touches the inner surface of the case core member 3 in a point contact manner only such that corner points of the upper flange 7 only contact the inner side surfaces of the case core member 3.
When the contact state between the upper flange 7 and the case core member 3 is varied in this way, a variation of a magnetic reluctance in a magnetic circuit defined by the square-flanged core member 2 and the case core member 3 occurs. The magnetic reluctance is considerably different when the case when outer surface of the upper flange 7 touches the case core member 3 as shown in FIG. 10B or FIG. 10C is compared with the case when the upper flange 7 is out of contact with the case core member 3. The conventional wire-wound inductor 1 thus suffers from a large variation in inductance.
To overcome the problems described above, preferred embodiments of the present invention provide a high-quality wire-wound inductor with minimal and negligible variations in inductance.
According to one preferred embodiment of the present invention, a wire-wound inductor preferably includes a substantially square-flanged core member having a wire-wound portion, around which a coil is wound, a substantially square flange provided at an end of the wire-wound portion, and a substantially cylindrical case core member accommodating the coil. The case core member is provided with a substantially square opening which receives the flange of the substantially square flange core member, and a corner abutment surface which the corner of the flange abuts and which is provided at a corner of an inner surface of the opening. The corner abutment surface may be a substantially planar surface or a substantially curved surface.
Since the opening of the case core member includes the corner abutment surfaces at the corners of its inner surface, the corners of the substantially square flange of the substantially square-flanged core member abut the respective corner abutment surfaces. The corner abutment surfaces prevent the flange of the substantially square-flanged core member from touching the case core member in a surface contact manner. Whether the flange of the substantially square-flanged core member is located at any position within the opening of the case core member, the flange of the substantially square-flanged core member remains out of contact with the case core member, or if in contact with the case core member at all, the flange of the square-flanged core member touches the case core member at a ridge defined by the apexes of the flange in a point contact manner only. This arrangement minimizes a variation in the magnetic reluctance of the magnetic circuit defined by the substantially square-flanged core member and the case core member.
Other features, elements, aspects and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the invention which refers to the accompanying drawings.